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A 4D tomographic ionospheric model to support PPP-RTK / German Olivares-Pulido in Journal of geodesy, vol 93 n° 9 (September 2019)  

Public [article]  inJournal of geodesy > vol 93 n° 9 (September 2019) . - pp 1673 - 1683 Titre : A 4D tomographic ionospheric model to support PPP-RTK Type de document : Article/Communication Auteurs : German Olivares-Pulido, Auteur ; M. Terkildsen, Auteur ; K. Arsov, Auteur ; et al., Auteur Année de publication : 2019 Article en page(s) : pp 1673 - 1683 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] modèle ionosphérique [Termes descripteurs IGN] modélisation 4D [Termes descripteurs IGN] positionnement cinématique en temps réel [Termes descripteurs IGN] positionnement ponctuel précis [Termes descripteurs IGN] tomographie par GPS Numéro de notice : A2019-508 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-019-01276-4 date de publication en ligne : 22/07/2019 En ligne : https://doi.org/10.1007/s00190-019-01276-4 Format de la ressource électronique : URL Article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=93793 [article]

Analysis of Galileo and GPS integration for GNSS tomography / Pedro Benevides in IEEE Transactions on geoscience and remote sensing, vol 55 n° 4 (April 2017)  

Public [article]  inIEEE Transactions on geoscience and remote sensing > vol 55 n° 4 (April 2017) . - pp 1936 - 1943 Titre : Analysis of Galileo and GPS integration for GNSS tomography Type de document : Article/Communication Auteurs : Pedro Benevides, Auteur ; G. Nico, Auteur ; J. Catalão, Auteur Année de publication : 2017 Article en page(s) : pp 1936 - 1943 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes descripteurs IGN] angle azimutal [Termes descripteurs IGN] atmosphère terrestre [Termes descripteurs IGN] données Galileo [Termes descripteurs IGN] humidité de l'air [Termes descripteurs IGN] intégration de données [Termes descripteurs IGN] Lisbonne [Termes descripteurs IGN] reconstruction 3D [Termes descripteurs IGN] réfraction atmosphérique [Termes descripteurs IGN] tomographie par GPS Résumé : (Auteur) Global Navigation Satellite System (GNSS) tomography provides 3-D reconstructions of atmosphere wet refractivity, related to water vapor. A simulated analysis of the integration of Global Positioning System and future Galileo data is presented. Atmospheric refractivity is derived from radiosonde data acquired over the Lisbon area. The impact of Galileo data on the tomographic reconstruction is assessed. Furthermore, horizontal anomalies are added to a reference vertical profile of atmospheric refractivity to reproduce low-level dry or wet air intrusions, a phenomenon commonly observed in meteorological data acquired by both radiosonde and satellites. The dependence of tomographic solution on the GNSS network density is also analyzed. Better reconstruction capabilities in the lower layers are observed when increasing the network density. Numéro de notice : A2017-170 Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern En ligne : http://dx.doi.org/10.1109/TGRS.2016.2631449 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=84714 [article]

Ionospheric tomography based on GNSS observations of the CMONOC: performance in the topside ionosphere / Zhe Yang in GPS solutions, vol 21 n° 2 (April 2017)  

Public [article]  inGPS solutions > vol 21 n° 2 (April 2017) . - pp 363 – 375 Titre : Ionospheric tomography based on GNSS observations of the CMONOC: performance in the topside ionosphere Type de document : Article/Communication Auteurs : Zhe Yang, Auteur ; Shuli Song, Auteur ; Wenhai Jiao, Auteur ; et al., Auteur Année de publication : 2017 Article en page(s) : pp 363 – 375 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes descripteurs IGN] Chine [Termes descripteurs IGN] Crustal Movement Observation Network of China [Termes descripteurs IGN] données localisées 3D [Termes descripteurs IGN] ionosphère [Termes descripteurs IGN] propagation ionosphérique [Termes descripteurs IGN] station GNSS [Termes descripteurs IGN] tomographie par GPS [Termes descripteurs IGN] voxel Résumé : (auteur) This study carries out a quantitative analysis of the performance of ionospheric tomography in the topside ionosphere, utilizing data of October 2011 collected from 260 Global Navigation Satellite System (GNSS) stations in the Crustal Movement Observation Network of China. This tomographic reconstruction with a resolution of 2° in latitude, 2° in longitude and 20 km in altitude has more than 70 % of voxels traversed by GPS raypaths and is able to provide reliable bottom parts of ionospheric profiles. Compared with the observations measured by the Defense Meteorological Satellite Program (DMSP) satellites (F16, F17 and F18) at an altitude of 830–880 km, the results show that there is an overestimation in the reconstructed plasma density at the DMSP altitude, and the reconstruction is better during daytime than nighttime. In addition, the reconstruction at nighttime also indicates a solar activity and latitudinal dependence. In summary, with respect to DMSP measurements, the daytime bias is on average from −0.32 × 105/cm3 to −0.28 × 105/cm3, while the nighttime bias is between −0.37 × 105/cm3 and −0.24 × 105/cm3, and the standard deviation at daytime and at nighttime is, respectively, 0.082 × 105/cm3 to 0.244 × 105/cm3 and 0.086 × 105/cm3 to 0.428 × 105/cm3. This study suggests that vertical ionospheric profiles from other sources, such as ionosondes or GNSS occultation satellites, should be incorporated into ground-based GNSS topside tomographic studies. Numéro de notice : A2017-212 Thématique : POSITIONNEMENT Nature : Article En ligne : http://dx.doi.org/10.1007/s10291-016-0526-0 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=85054 [article]

Ionospheric tomography using GNSS: multiplicative algebraic reconstruction technique applied to the area of Brazil / Fabricio Dos Santos Prol in GPS solutions, vol 20 n° 4 (October 2016)  

Public [article]  inGPS solutions > vol 20 n° 4 (October 2016) . - pp 807 - 814 Titre : Ionospheric tomography using GNSS: multiplicative algebraic reconstruction technique applied to the area of Brazil Type de document : Article/Communication Auteurs : Fabricio Dos Santos Prol, Auteur ; Paulo de Oliveira Camargo, Auteur Année de publication : 2016 Article en page(s) : pp 807 - 814 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes descripteurs IGN] Brésil [Termes descripteurs IGN] code GNSS [Termes descripteurs IGN] International Reference Ionosphere [Termes descripteurs IGN] modèle ionosphérique [Termes descripteurs IGN] multiplicative algebraic reconstruction technique [Termes descripteurs IGN] phase GNSS [Termes descripteurs IGN] récepteur GNSS [Termes descripteurs IGN] teneur totale en électrons [Termes descripteurs IGN] tomographie par GPS Résumé : (Auteur) Experimental analysis was performed using multiplicative algebraic reconstruction technique (MART) to map the ionosphere over Brazil. Code and phase observations from the global navigation satellite system (GNSS) together with the international reference ionosphere (IRI) enabled the estimation of ionospheric profiles and total electron content (TEC) over the entire region. Twenty-four days of data collected from existing ground-based GNSS receivers during the recent solar maximum period were used to analyze the performance of the MART algorithm. The results were compared with four ionosondes. It was demonstrated that MART estimated the electron density peak with the same degree of accuracy as the IRI model in regions with appropriate geometrical coverage by GNSS receivers for tomographic reconstruction. In addition, the slant TEC, as estimated with MART, presented lower root-mean-square error than the TEC calculated by ionospheric maps available from the International GNSS Service (IGS). Furthermore, the daily variations of the ionosphere were better represented with the algebraic techniques, compared to the IRI model and IGS maps, enabling a correlation of the elevation of the ionosphere at higher altitudes with the equatorial ionization anomaly intensification. The tomographic representations also enabled the detection of high vertical gradients at the same instants in which ionospheric irregularities were evident. Numéro de notice : A2016--030 Thématique : POSITIONNEMENT Nature : Article En ligne : http://dx.doi.org/10.1007/s10291-015-0490-0 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=83932 [article]

Water vapor tomography using global navigation satellites systems / Donat Perler (2012)    

Public Titre : Water vapor tomography using global navigation satellites systems Type de document : Thèse/HDR Auteurs : Donat Perler, Auteur Editeur : Zurich : Schweizerischen Geodatischen Kommission / Commission Géodésique Suisse Année de publication : 2012 Collection : Geodätisch-Geophysikalische Arbeiten in der Schweiz, ISSN 0257-1722 num. 84 Importance : 188 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-908440-30-7 Note générale : Bibliographie Doctoral Thesis Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes descripteurs IGN] atmosphère terrestre [Termes descripteurs IGN] données GNSS [Termes descripteurs IGN] données météorologiques [Termes descripteurs IGN] modélisation spatiale [Termes descripteurs IGN] positionnement par GNSS [Termes descripteurs IGN] rayonnement électromagnétique [Termes descripteurs IGN] temps réel [Termes descripteurs IGN] teneur en vapeur d'eau [Termes descripteurs IGN] tomographie par GPS [Termes descripteurs IGN] vapeur d'eau Résumé : (Auteur) Water vapor plays an important role in the atmosphere. It is involved in many atmospheric processes and is a major contributor to the atmospheric energy budget and as such is a key quantity in numerical weather prediction (NWP) models. In recent years, NWP models gain in importance in hazard mitigation. But to provide precise quantitative forecasts, especially with respect to precipitation, we need accurate knowledge of the water vapor distribution in the atmosphere. Ground-based Global Navigation Satellite System (GNSS) tomography is a technique which can provide highly resolved and accurate water vapor profiles in space and time. The main objective of this thesis is to develop new tomographic algorithms which fulfill the requirements to assimilate refractivity measurements derived from GNSS into NWP models. A new tomography software called AWATOS 2 has been implemented. It is an assimilation system for point and integrated refractivity measurements. The tomographic model in AWATOS 2 is formulated as a Kalman filter and different voxel parameterizations are provided. The new trilinear and spline-based parameterizations allow a more accurate representation of the refractivity field without considerably increasing the number of unknowns. Advantages of these new parameterizations are a) more accurate results, b) point observations need not to be interpolated to the voxel centers and c) the tomographic solutions are at least C0-continuous in space. The stochastic prediction model implemented in AWATOS 2 relies on in-situ measurements and NWP model data. The prediction model is evaluated and adjusted with respect to data from the high-resolution NWP model COSMO-2 and from balloon soundings in Europe. In addition, AWATOS 2 provides a sophisticated simulation framework to carry out synthetic tests based on simple refractivity fields and on NWP model data. The algorithms of AWATOS 2 are assessed with synthetic tests and with real data in a longterm study using one year of data. The synthetic tests have confirmed the theoretical properties of the model such as a bias-free solution in case of bias-free input data, fast convergence rates, and the capability to resolve vertical structures in the wet refractivity field. In the long-term study, a root-mean-square (RMS) error of 3.0 ppm (0.4 gm3 absolute humidity) is achieved with respect to the NWP model COSMO-7. The investigations have shown that the newly introduced voxel parameterizations lead to significantly more accurate results than the classical constant parameterization. The improvements are about 15% with respect to balloon soundings and 5% with respect to NWP analysis data. The performance of the trilinear and spline-based parameterizations are similar. Further investigations have revealed the importance of a bias correction model. A newly developed bias correction model has decreased the RMS error with respect to the NWP model analysis from 4.9 ppm (0.7 gm3) to 3.0 ppm (0.4 gm3) using the spline parameterization. For the other parameterizations, the improvements are significantly smaller. The systematic differences corrected here are mainly caused by a) systematic differences between GPS tropospheric path delays and the NWP model data and b) by discretization errors. Another error source is related to the departure of the NWP model’s topography from the true one which can amount to several hundred meters in alpine areas. Investigations have shown that processes near the Earth’s surface have a strong impact on the wet refractivity. Therefore, differences between the true topography and that of the NWP model can cause substantial errors. This topic has to be addressed if GNSS observations are assimilated into NWP models in complex terrain. Considerable progress has been made in the field of low-cost GNSS receivers in recent years allowing to build dense networks at low costs. Furthermore, the existing GNSSs are improved and new ones are being launched. These developments offer new possibilities in GNSS tomography. With error analyses, the potential of such improvements for GNSS tomography have been investigated The use of GPS together with Galileo has the potential to improve the formal accuracy of the GNSS tomography by 10-15% compared to a GPS-only solution. In Switzerland, equipping the SwissMetNet with GNSS receivers would increase the number of GNSS stations from 31 to 91. This would improve the formal accuracy of the tomographic solution by about 20-25%. The investigations have shown that the improvements obtained by a more dense network and additional GNSSs are cumulative. Placing the stations on different altitudes and choosing locations with good satellite visibility are important to achieve accurate results and should be considered in the design of GNSS networks. All investigations have demonstrated that accurate 4D distributions of the wet refractivity in the troposphere can be estimated with GNSS tomography. The work has also revealed the possibilities and limitations of GNSS tomography in view of the assimilation into NWP models and proposes solution strategies to overcome the limitations. Note de contenu : 1 Introduction 1.1 Significance of tropospheric water vapor measurements 1.2 A short review of the research in GNSS tomography 1.3 Objectives and structure of the thesis 2 Introduction to the propagation of radio waves in the atmosphere 2.1 Propagation of radio waves in the atmosphere 2.2 Modeling the path delay 3 GNSS tomography with the software package AWATOS 2 3.1 Overview of AWATOS 2 3.2 Preprocessing of GNSS double difference delays 3.3 Discretization of the refractivity field and parameterization 3.4 Modeling the refractivity field with the Kalman filter approach 3.5 Simulation capabilities in AWATOS 2 4 Overview of the data sets 4.1 GPS data 4.2 Balloon soundings 4.3 Synoptic network SwissMetNet 4.4 Numerical weather prediction model COSMO 5 Description of the wet refractivity field 5.1 Tempo-spatial variation of the wet refractivity field 5.2 Discretization Error 5.3 Representation of the discretization error . 5.4 Investigations of the process noise using a random walk model 5.5 Conclusions 6 Comparison of balloon sounding data and GNSS-derived zenith path delays 6.1 Error budget of meteorological sensors 6.2 Intercomparison between zenith path delays of different sources 6.3 Conclusions 7 Potential of new GNSSs and dense networks in view of GNSS tomography 7.1 Configurations 7.2 Methods 7.3 Results and discussion 7.4 Conclusions 8 Simulation-based evaluation of the new tomographic algorithms 8.1 Theoretical considerations of the resolvability of vertical structures 8.2 Experiments with simulated data 8.3 Conclusions 9 Evaluation of the GPS tomography with a long-term study 9.1 Configuration and evaluation methods 9.2 Results and discussion 9.3 Bias correction model and its evaluation 9.4 Conclusions 10 Conclusions 11 Outlook Numéro de notice : 15546 Thématique : POSITIONNEMENT Nature : Thèse étrangère DOI : 10.3929/ethz-a-006875504 En ligne : http://dx.doi.org/10.3929/ethz-a-006875504 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=62758

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